Story of a cursed rotary
04-01-23, 07:35 AM
#26
Racing Rotary Since 1983
iTrader: (6)
while this post isn't the final final on this motor it is relevant.
a close inspection of the rotor housings showed they did not need to be honed. they did show apex seal lift at the spark plug location. spark plug mountain.
it is my contention that most "warped" apex seals are worn not warped. you do not need a digital mic or a vernier caliper to spec this. all you have to do is run your finger on the side of the seal from the bottom upward. if they are worn you will feel a ledge at the start of the crown. this is displaced metal from the contact surface of the seal. it is displaced by the distention from the spark plug boss and the close of the exhaust port.
too much heat and too little lube.
colder plugs (though he had 11s), proper timing, proper lube, proper BREAK IN, low backpressure, proper fuel delivery solve the problem.
in this case the motor was fine as to comp in the front and not fine in the rear.
surprise surprise, the front apex seals had NO ledging, while you could shave with the rears.
the motor did 120 in the front and rear after reassembly so no housing damage.
the upcoming challenge will be not to have a repeat.
it will start with a lengthy break in and keeping the engine away from a dyno.
as is often the case, the apex seals were the victim, not the culprit.
to be continued.
a close inspection of the rotor housings showed they did not need to be honed. they did show apex seal lift at the spark plug location. spark plug mountain.
it is my contention that most "warped" apex seals are worn not warped. you do not need a digital mic or a vernier caliper to spec this. all you have to do is run your finger on the side of the seal from the bottom upward. if they are worn you will feel a ledge at the start of the crown. this is displaced metal from the contact surface of the seal. it is displaced by the distention from the spark plug boss and the close of the exhaust port.
too much heat and too little lube.
colder plugs (though he had 11s), proper timing, proper lube, proper BREAK IN, low backpressure, proper fuel delivery solve the problem.
in this case the motor was fine as to comp in the front and not fine in the rear.
surprise surprise, the front apex seals had NO ledging, while you could shave with the rears.
the motor did 120 in the front and rear after reassembly so no housing damage.
the upcoming challenge will be not to have a repeat.
it will start with a lengthy break in and keeping the engine away from a dyno.
as is often the case, the apex seals were the victim, not the culprit.
to be continued.
04-01-23, 02:34 PM
#27
In case the heat in the rear was due to fuel imbalance, I would label all the fuel injectors (so you know which were from the front rotor and which were feeding the rear rotor) then find a place that can flow test them before and after cleaning them. Near me that's SubieTech ( https://subietech.com/fuel-injection/ ), and if you ask local tuners you can usually find a local shop that can do it. It doesn't need to be a rotary shop, fuel injectors are fuel injectors and it's good to support local shops when possible. When I say 'fuel imbalance' I mean the single wideband sensor most people use is showing the average air/fuel ratio in the downpipe after the exhaust from the two rotors has merged. When the wideband sensor shows Lambda = 0.75 that might be Lambda=0.65 from the front rotor and Lambda=0.85 from the rear. The exhaust gases mix together before reaching the sensor, so it's difficult to know without adding sensors in the primary exhaust runners. Personally I doubt that's a big problem but the cost of flow-testing or even adding two more wideband O2 gauges is small compared to an engine failure.
I agree that coolant flow makes good sense, seems more likely than fuel injector flow differences. If you look at the cooling system closely, cold coolant from the radiator gets pumped through the front rotor passages first, (where it heats up) before it goes to the rear rotor passages. Heat transfer is related to the difference in temperature, so the already-warm coolant is not able to extract as much heat from the rear rotor as it extracted from the front rotor. As the engine warms up, this problem will be exacerbated because the rear housing needs more heat removed but the coolant temp is even hotter because more heat has been transferred from the front housing. I think a 'too cold' thermostat or a few small holes drilled in the OEM thermostat is a cheap way to add some more safety margin, assuming the engine runs near thermostat temps. Increased coolant flow should help too, from an upgraded pump.
In addition, Barry Bordes has posted some great photos showing modifications that can be performed to correct a cooling passage design flaw and improve coolant flow near the hottest parts of the engine: https://www.rx7club.com/3rd-generati...em-fix-989811/
I agree that coolant flow makes good sense, seems more likely than fuel injector flow differences. If you look at the cooling system closely, cold coolant from the radiator gets pumped through the front rotor passages first, (where it heats up) before it goes to the rear rotor passages. Heat transfer is related to the difference in temperature, so the already-warm coolant is not able to extract as much heat from the rear rotor as it extracted from the front rotor. As the engine warms up, this problem will be exacerbated because the rear housing needs more heat removed but the coolant temp is even hotter because more heat has been transferred from the front housing. I think a 'too cold' thermostat or a few small holes drilled in the OEM thermostat is a cheap way to add some more safety margin, assuming the engine runs near thermostat temps. Increased coolant flow should help too, from an upgraded pump.
In addition, Barry Bordes has posted some great photos showing modifications that can be performed to correct a cooling passage design flaw and improve coolant flow near the hottest parts of the engine: https://www.rx7club.com/3rd-generati...em-fix-989811/
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j9fd3s (04-02-23)
04-02-23, 09:42 AM
#28
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i went back and re-read all of the "warped seal" threads i could find. i was just looking for a common denominator and there are a few;
the first is the story, engine does break in fine, usually break in is really long (we used to let the race cars fast idle for 45minutes!) and then after break in is declared over. car goes to dyno or track or something and engine dies right there.
Second is that the "average problem build" is usually a big one, its usually engine, ecu, ignition, AI, etc etc. Complexity is a big contributor to the problem, IMO.
Three. these seals are showing heavy wear and not warping. although the factory seals are crowned so they essentially start warped and then wear straight.
its totally possible that these problem seals aren't right out of the box, this gets mentioned in a couple of old threads. remember Apex seals have 4 dimensions, Length, Width, Height, and Crown.
the first is the story, engine does break in fine, usually break in is really long (we used to let the race cars fast idle for 45minutes!) and then after break in is declared over. car goes to dyno or track or something and engine dies right there.
Second is that the "average problem build" is usually a big one, its usually engine, ecu, ignition, AI, etc etc. Complexity is a big contributor to the problem, IMO.
Three. these seals are showing heavy wear and not warping. although the factory seals are crowned so they essentially start warped and then wear straight.
its totally possible that these problem seals aren't right out of the box, this gets mentioned in a couple of old threads. remember Apex seals have 4 dimensions, Length, Width, Height, and Crown.
04-02-23, 10:48 AM
#29
Racing Rotary Since 1983
iTrader: (6)
"engine does break in fine, usually break in is really long (we used to let the race cars fast idle for 45minutes!) and then after break in is declared over. car goes to dyno or track or something and engine dies right there."
i am increasingly convinced by my experience that breakin IS a very important component of producing a longer lived engine. i recommend a minimum of 500 miles, lots of heat cycles. break in oil. my race engines were built by Roger Mandeville and Daryl Drummond and were run over 12 hours on an engine dyno.
" "average problem build" is usually a big one, its usually engine, ecu, ignition, AI, etc etc. Complexity is a big contributor to the problem, IMO."
most builds today are single turbos as the dreadful twin setup has spun itself into oblivion... so yes, you can consider them "big"
the challenge is better described as the builds are generating higher combustion chamber pressure and higher combustion chamber heat. it is a challenge and if you want to descibe it as complex that also works. we all know that as you up the CCH and CCP there can be no weak links in the chain. you are totally correct as to describing it as complex. it is complex because you have to do everything right. if you are not up for the challenge simply stay OE.
" these seals are showing heavy wear and not warping. although the factory seals are crowned so they essentially start warped and then wear straight.
its totally possible that these problem seals aren't right out of the box, this gets mentioned in a couple of old threads. remember Apex seals have 4 dimensions, Length, Width, Height, and Crown."
not buying that the seals aren't right out of the box. the primary message on my website is that all our engines are more stressed (even at 350 hp) than we think so you have to have ALL the systems right. i maintain that in the vast majority of apex seal problems they are the victim not the culprit.
i am increasingly convinced by my experience that breakin IS a very important component of producing a longer lived engine. i recommend a minimum of 500 miles, lots of heat cycles. break in oil. my race engines were built by Roger Mandeville and Daryl Drummond and were run over 12 hours on an engine dyno.
" "average problem build" is usually a big one, its usually engine, ecu, ignition, AI, etc etc. Complexity is a big contributor to the problem, IMO."
most builds today are single turbos as the dreadful twin setup has spun itself into oblivion... so yes, you can consider them "big"
the challenge is better described as the builds are generating higher combustion chamber pressure and higher combustion chamber heat. it is a challenge and if you want to descibe it as complex that also works. we all know that as you up the CCH and CCP there can be no weak links in the chain. you are totally correct as to describing it as complex. it is complex because you have to do everything right. if you are not up for the challenge simply stay OE.
" these seals are showing heavy wear and not warping. although the factory seals are crowned so they essentially start warped and then wear straight.
its totally possible that these problem seals aren't right out of the box, this gets mentioned in a couple of old threads. remember Apex seals have 4 dimensions, Length, Width, Height, and Crown."
not buying that the seals aren't right out of the box. the primary message on my website is that all our engines are more stressed (even at 350 hp) than we think so you have to have ALL the systems right. i maintain that in the vast majority of apex seal problems they are the victim not the culprit.
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